U.S. patent application number 10/250716 was filed with the patent office on 2004-03-25 for method and device for controlling an exhaust treatment system.
Invention is credited to Mahr, Bernd, Ripper, Wolfgang, Wickert, Stefan.
Application Number | 20040055284 10/250716 |
Document ID | / |
Family ID | 7669899 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040055284 |
Kind Code |
A1 |
Ripper, Wolfgang ; et
al. |
March 25, 2004 |
Method and device for controlling an exhaust treatment system
Abstract
A device and a method for controlling an exhaust-gas
aftertreatment system, in particular for an internal combustion
engine, is described. The exhaust-gas aftertreatment system
includes at least one catalytic converter. A preselectable quantity
of reducing agent is supplied to the exhaust-gas aftertreatment
system as a function of the state of the internal combustion engine
and/or the exhaust-gas aftertreatment system. The quantity of
reducing agent supplied is adjusted.
Inventors: |
Ripper, Wolfgang;
(Stuttgart, DE) ; Mahr, Bernd; (Plochingen,
DE) ; Wickert, Stefan; (Albershausen, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7669899 |
Appl. No.: |
10/250716 |
Filed: |
November 20, 2003 |
PCT Filed: |
December 22, 2001 |
PCT NO: |
PCT/DE01/04923 |
Current U.S.
Class: |
60/286 ; 60/285;
60/295; 60/301 |
Current CPC
Class: |
F01N 2560/021 20130101;
F01N 2610/02 20130101; F01N 2900/08 20130101; Y02T 10/12 20130101;
F01N 2900/0408 20130101; B01D 53/9409 20130101; B01D 53/8625
20130101; F01N 2560/06 20130101; F01N 2610/03 20130101; F01N
2610/146 20130101; B01D 53/8696 20130101; F01N 3/208 20130101; Y02T
10/24 20130101; F01N 2560/026 20130101; B01D 53/9495 20130101; F01N
2240/40 20130101; F01N 13/0097 20140603 |
Class at
Publication: |
060/286 ;
060/285; 060/295; 060/301 |
International
Class: |
F01N 003/00; F01N
003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 2001 |
DE |
101 00 420.6 |
Claims
What is claimed is:
1. A method for controlling an exhaust-gas aftertreatment system,
in particular for an internal combustion engine, the exhaust-gas
aftertreatment system comprising at least one catalytic converter,
a preselectable quantity of reducing agent being supplied to the
exhaust-gas aftertreatment system as a function of the state of the
internal combustion engine and/or the exhaust-gas aftertreatment
system, wherein the quantity of reducing agent supplied is
adjusted.
2. The method as recited in claim 1, wherein a measured variable
characterizing the effect of the exhaust-gas aftertreatment system
is detected.
3. The method as recited in one of the preceding claims, wherein
the measured variable detected depends on the concentration of
substances which are only partially converted or are not converted
at all in the exhaust-gas aftertreatment system, the concentration
of substances required for the conversion, and/or the concentration
of unwanted intermediates formed.
4. The method as recited in one of the preceding claims, wherein
the measured variable is compared with expected values in certain
states of the internal combustion engine and/or the exhaust-gas
aftertreatment system, and the quantity of reducing agent is
corrected on the basis of this comparison.
5. The method as recited in one of the preceding claims, wherein a
first variable, characterizing the quantity of ammonia in the
exhaust gas downstream from the exhaust-gas aftertreatment system,
is detected, the quantity of reducing agent being decreased when
the first variable exceeds an upper threshold value, and/or the
quantity of reducing agent being increased when the first variable
falls below a lower threshold value.
6. The method as recited in one of the preceding claims, wherein a
second variable, which characterizes the quantity of nitrogen
oxides in the exhaust gas downstream from the exhaust-gas
aftertreatment system, is detected, the quantity of reducing agent
being decreased when the second variable falls below a lower
threshold value and/or the quantity of reducing agent being
increased when the second variable exceeds an upper threshold
value.
7. The method as recited in one of the preceding claims, wherein
the quantity of reducing agent is decreased when the first variable
exceeds an upper threshold value, and/or the quantity of reducing
agent is increased when the second variable exceeds an upper
threshold value.
8. A device for controlling an exhaust-gas aftertreatment system,
in particular for an internal combustion engine, the exhaust-gas
aftertreatment system comprising at least one catalytic converter,
a predefinable quantity of reducing agent being supplied to the
exhaust-gas aftertreatment system as a function of the state of the
internal combustion engine and/or the exhaust-gas aftertreatment
system, wherein means are provided for adjusting the quantity of
reducing agent supplied.
9. A computer program having program code means for performing all
steps of any of claims 1 through 11 when the program is executed on
a computer, in particular a control unit for an internal combustion
engine.
10. A computer program product having program code means stored on
a computer-readable data medium for performing the method as
recited in any of claims 1 through 11 when the product is executed
on a computer, in particular a control unit for an internal
combustion engine.
Description
BACKGROUND INFORMATION
[0001] The present invention relates to a method and a device for
controlling an exhaust-gas aftertreatment system.
[0002] A method and a device for controlling an exhaust-gas
aftertreatment system are known from German Patent 199 03 439,
where a method and a device for controlling an exhaust-gas
aftertreatment system are described, the exhaust-gas aftertreatment
system including at least one catalytic converter, and a
predefinable quantity of reducing agent being supplied to the
exhaust-gas aftertreatment system as a function of the state of the
internal combustion engine and/or the exhaust-gas aftertreatment
system. The quantity of reducing agent supplied is preferably
determined on the basis of operating characteristics of the
internal combustion engine, such as the rotational speed and the
quantity of fuel injected as well as variables which characterize
the state of the exhaust-gas aftertreatment system, e.g., the
exhaust gas temperature upstream from, within, and/or downstream
from the exhaust-gas aftertreatment system.
[0003] When using urea as the reducing agent in particular,
metering of the reducing agent is problematical. If too little
reducing agent is supplied to the exhaust-gas aftertreatment
system, the result is that nitrogen oxides are not adequately
converted and then they enter the environment. If too much reducing
agent is supplied, in particular in the case of metering a urea
solution, unwanted substances such as, e.g., ammonia will enter the
environment. This emission of ammonia must be reliably prevented.
Therefore, the usual procedure tends to be to meter too little
reducing agent. In other words, the quantity of reducing agent is
predefined so that tolerances in the area of the internal
combustion engine, the exhaust-gas aftertreatment system or the
metering system for metering the reducing agent do not result in
the presence of ammonia in the exhaust gas.
ADVANTAGES OF THE INVENTION
[0004] By adjusting the quantity of reducing agent supplied, the
quantity of reducing agent supplied may be set to yield only
minimal nitrogen oxide emissions, with the emission of ammonia
being reliably prevented.
[0005] It is particularly advantageous if the adjustment is based
on a measured variable which characterizes the effect of the
exhaust-gas aftertreatment system. Such a measured variable is
supplied, for example, by a sensor which detects nitrogen oxide
emissions and/or a sensor which detects ammonia emissions. In the
case of systems which work with other reducing agents, other
sensors will be used accordingly.
[0006] Sensors which detect measured values characterizing the
effect of the exhaust-gas aftertreatment system are preferably
used. These measured variables may depend on the concentration of
various substances. These are substances that are not converted at
all or are converted only partially in the exhaust-gas
aftertreatment system, substances required for the reaction, and/or
intermediates. It is preferable to use sensors which detect
substances which occur in the exhaust gas system downstream from
the exhaust-gas aftertreatment system and are necessary for the
reaction in the exhaust-gas aftertreatment system or are formed as
intermediates during the reaction. It is particularly advantageous
to use a nitrogen oxide sensor whose different variants may be used
for exhaust-gas aftertreatment. Furthermore, it may be used for
other functions in the area of control of the internal combustion
engine and/or the exhaust-gas aftertreatment system. In the case of
systems using urea as the reducing agent, an ammonia sensor is
advantageous.
[0007] It is particularly advantageous that adjustment is performed
only in certain operating states of the internal combustion engine
and/or the exhaust-gas aftertreatment system. In these particular
operating states, the measured variable(s) is/are compared with
values to be expected, and the quantity of reducing agent is
corrected on the basis of this comparison.
[0008] In a first embodiment, a first variable characterizing the
quantity of ammonia in the exhaust gas downstream from the
exhaust-gas aftertreatment system is detected, the quantity of
reducing agent being decreased when the first variable exceeds an
upper threshold value and/or the quantity of reducing agent being
increased when the first variable falls below a lower threshold
value.
[0009] In a second embodiment, a second variable characterizing the
quantity of nitrogen oxides in the exhaust gas downstream from the
exhaust-gas aftertreatment system is detected, the quantity of
reducing agent being decreased when the second variable falls below
a lower threshold value and/or the quantity of reducing agent being
increased when the second variable exceeds an upper threshold
value.
[0010] A particularly accurate control is obtained with an
embodiment in which the quantity of reducing agent is decreased
when the first variable exceeds an upper threshold value and/or the
quantity of reducing agent is increased when the second variable
exceeds an upper threshold value.
[0011] In addition, implementations in the form of a computer
program having program code means and in the form of a computer
program product having program code means are particularly
important. The computer program according to the present invention
has program code means for performing all the steps of the method
according to the present invention when the program is executed on
a computer, in particular a control unit for an internal combustion
engine of a motor vehicle. In this case, the invention is
implemented by a program stored in the control unit, so that this
control unit, equipped with the program, constitutes the present
invention in the same way as does the method for whose execution
the program is suitable. The computer program product according to
the present invention has program code means which are stored on a
computer-readable data medium for executing the method according to
the present invention when this program product is run on a
computer, in particular a control unit for an internal combustion
engine of a motor vehicle. Thus, in this case, the invention is
implemented by a data medium, so that the method according to the
present invention may be implemented when the program product
and/or the data medium is integrated into a control unit for an
internal combustion engine of a motor vehicle in particular. The
data medium and/or the computer program product may be in
particular an electric memory medium, e.g., a read-only memory
(ROM), an EPROM or a permanent electric memory such as a CD-ROM or
DVD.
[0012] Advantageous and expedient embodiments and refinements of
the present invention are characterized in the subclaims.
DRAWING
[0013] The present invention is explained in greater detail below
on the basis of embodiments illustrated in the drawing.
[0014] FIG. 1 shows a block diagram of the device according to the
present invention;
[0015] FIG. 2 shows a detailed diagram of the device according to
the present invention in the form of a block diagram; and
[0016] FIG. 3 shows a flow chart to illustrate the procedure
according to the present invention.
[0017] FIG. 1 shows the essential elements of an exhaust-gas
aftertreatment system of an internal combustion engine. Internal
combustion engine 100 receives fresh air through a fresh air line
105. Exhaust gases from internal combustion engine 100 enter the
environment through an exhaust gas line 110. An exhaust-gas
aftertreatment system 115 is provided in the exhaust gas line. This
is preferably a catalytic converter. In addition, it is possible
for a plurality of catalytic converters to be provided for
different pollutants, or for a combination of at least one
catalytic converter and one particle filter to be used.
[0018] In the preferred embodiment, exhaust-gas aftertreatment
system 115 includes one catalytic converter or three catalytic
converters in which preferably three reactions take place. The
aqueous urea solution supplied with control element 182 is
converted to ammonia NH.sub.3 in a first hydrolysis catalytic
converter 115a. The actual reaction takes place in downstream SCR
catalytic converter 115b, where nitrogen oxides and ammonia react
to form nitrogen and water. Unconsumed ammonia is oxidized in
downstream oxidation catalytic converter 115c.
[0019] In alternative embodiments in which other reducing agents
are used, other catalytic converters may also be used or individual
catalytic converters may be omitted. The hydrolysis catalytic
converter in particular may be omitted when the reducing agent is
supplied directly.
[0020] In addition, a control unit 170 including at least one
engine control unit 175 and an exhaust-gas aftertreatment control
unit 172 is also provided. Engine control unit 175 sends triggering
signals to a fuel metering system 180. Exhaust-gas aftertreatment
control unit 172 exchanges signals with engine control unit 175.
Furthermore, exhaust-gas aftertreatment control unit 172 sends
triggering signals to an actuator element 182 situated in the
exhaust gas line upstream from or in the exhaust-gas aftertreatment
system.
[0021] In addition, various sensors which supply signals to the
exhaust-gas aftertreatment control unit and the engine control unit
may also be provided. For example, at least one first sensor 194
may be provided to supply signals characterizing the state of the
internal combustion engine. A second sensor 177 supplies signals
characterizing the state of fuel metering system 180.
[0022] A temperature sensor 191 detects a temperature variable T
which characterizes the temperature of the exhaust-gas
aftertreatment system. Temperature sensor 191 is preferably
situated downstream from catalytic converter 115. A sensor 193
preferably detects a nitrogen oxide concentration in the exhaust
gas downstream from the exhaust-gas aftertreatment system. An
emission sensor 192 detects an NH.sub.3 signal which characterizes
the quantity of ammonia in the exhaust gas downstream from the
exhaust-gas aftertreatment system. It is particularly advantageous
if the emission sensor is situated between SCR catalytic converter
115b and oxidation catalytic converter 115c. An emission sensor 192
or a sensor 193 which detects the nitrogen oxide concentration in
the exhaust gas downstream from the exhaust-gas aftertreatment
system is preferably provided.
[0023] Exhaust-gas aftertreatment control unit 172 preferably
receives the output signals of sensors 191, 192 and 193. Engine
control unit 175 preferably receives the output signals of second
sensor 177. Other sensors not shown here may also be provided to
characterize a signal related to the driver's intent or other
ambient conditions or engine operating states.
[0024] It is particularly advantageous if the engine control unit
and the exhaust-gas aftertreatment control unit form one structural
unit. However, it is also possible for these units to be designed
as two physically separate control units.
[0025] The procedure according to the present invention is
described below using the example of a reduction catalytic
converter, which is used in particular with direct-injection
internal combustion engines. However, the procedure according to
the present invention is not limited to this application but
instead may also be used with other internal combustion engines
having an exhaust-gas aftertreatment system. In particular, it may
be used with exhaust-gas aftertreatment systems in which a
catalytic converter and a particle filter are combined.
[0026] On the basis of the sensor signals received, engine control
175 computes trigger signals to be applied to fuel metering system
180, which then meters the proper quantity of fuel for internal
combustion engine 100. During combustion, nitrogen oxides may be
formed in the exhaust gas. They are converted into nitrogen and
water by reduction catalytic converter 115b in exhaust-gas
aftertreatment system 115. To do so, a reducing agent must be
supplied to the exhaust gas upstream from the exhaust-gas
aftertreatment system. In the embodiment illustrated here, this
reducing agent is supplied to the exhaust gas via actuator member
182. Ammonia is preferably used as the reducing agent; it is formed
from a urea solution in hydrolysis catalytic converter 115a.
[0027] Actuator element 182 is preferably situated in exhaust gas
line 110. However, it may also be mounted in or on the exhaust-gas
aftertreatment system, in particular on hydrolysis catalytic
converter 115a.
[0028] In the embodiment described below, an aqueous urea solution
is supplied to the exhaust-gas aftertreatment system with actuator
element 182. The aqueous urea solution is hereinafter referred to
as the reducing agent.
[0029] FIG. 2 shows exhaust-gas aftertreatment control unit 172 in
greater detail. Elements already described in conjunction with FIG.
2 are labeled here with the same reference numbers. Essentially,
exhaust-gas aftertreatment control unit 172 includes a signal
preselection unit 200 and a correction value determination unit
220. Output signal H0 of signal value preselection goes to a node
210 along with output signal K of the correction value
preselection. Actuator element 182 is triggered with output signal
H of node 210.
[0030] Correction value determination unit 220 processes the output
signals of sensor 193, which detects the nitrogen oxide
concentration in the exhaust gas downstream from the exhaust-gas
aftertreatment system and/or the output signal of emission sensor
192, which supplies an NH.sub.3 signal that characterizes the
quantity of ammonia in the exhaust gas downstream from the
exhaust-gas aftertreatment system. Furthermore, correction value
determination unit 220 receives operating characteristics such as
rotational speed N and quantity of fuel QK injected into the
internal combustion engine.
[0031] Signal preselection unit 200 receives various operating
characteristics, e.g., rotational speed N, quantity of fuel QK
injected into the internal combustion engine, and various
temperature variables T, which characterize in particular the
exhaust gas temperature upstream from, within and/or downstream
from exhaust-gas aftertreatment system 115.
[0032] Based on these variables, the signal preselection unit
calculates a triggering signal H0 with which actuator element 182
is triggered. Values H0 which determine the triggering signal for
actuator element 182 are preferably stored in one or more engine
characteristics maps as a function of the input variables. It is
possible to provide for variables stored in the engine
characteristics map to be corrected on the basis of various
operating characteristics.
[0033] A procedure for preselecting triggering signal H0 is
described in German Patent 199 03 439, for example. However, the
procedure according to the present invention is not limited to this
type of determination of the triggering signals for actuator
element 182. It may also be applied in a similar manner to other
procedures for determining the triggering signal or for determining
other variables which determine this triggering signal. It is
essential that signal preselection unit 200 preselects the
triggering signal for actuator element 182 and/or a variable which
determines the quantity of reducing agent to be supplied to the
exhaust-gas aftertreatment system.
[0034] Since internal combustion engines and/or exhaust-gas
aftertreatment systems usually exhibit tolerances, the values
stored in signal preselection unit 200 are very inaccurate, i.e.,
are also subject to high tolerances. In other words, compromises
must be made with regard to emissions of ammonia and/or nitrogen
oxides.
[0035] To be able to achieve a further reduction in emissions
and/or unwanted exhaust gas constituents, a specific adjustment of
the metering system to the particular internal combustion engine
and/or to the particular exhaust-gas aftertreatment system is
performed according to the present invention. To do so, sensor 192
situated in or downstream from the exhaust-gas aftertreatment
system is used to detect nitrogen oxide emissions or ammonia
emissions.
[0036] The emissions thus detected are compared with suitable
setpoint values which are to be achieved. The values stored in the
signal preselection unit are corrected when limiting values are
exceeded and/or not met. This is accomplished by correction value
preselection unit 220, which preselects a correction value K for
the embodiment illustrated here, this correction value being
associated with the output signal H0 of signal preselection unit
for forming triggering signal H. An additive or multiplicative
correction is preferably performed.
[0037] This compensation is preferably performed at the time of
initial operation of the vehicle and then at regular intervals
and/or when certain states of the internal combustion engine and/or
exhaust-gas aftertreatment system occur.
[0038] FIG. 3 illustrates the functioning of correction value
determination unit 220 in greater detail. In a first step 310, the
operating point of the internal combustion engine and/or the
exhaust-gas aftertreatment system is detected. For example,
rotational speed N and quantity of fuel injected QK of the internal
combustion engine are analyzed. Furthermore, it is possible to
provide for the reading of an elapsed time meter and/or an odometer
which detects the total distance traveled.
[0039] Then in step 320 a check is performed to ascertain whether
the prevailing state is one in which adjustment is possible and
appropriate. Such operating states include in particular
steady-state operating states in which the values detected are
constant over a certain period of time. This is necessary because
the exhaust-gas aftertreatment system has a relatively long dead
time. This means that when there are changes in the operating
state, they have an effect only after a certain lag time.
[0040] An adjustment is performed only in such operating states in
which the system is in a stable state, i.e., a certain period of
time should have elapsed since the last change in operating
characteristics. In addition, it is possible to provide for the
adjustment to take place only when the internal combustion engine
and/or the exhaust-gas aftertreatment system is at certain
operating points. These operating points are defined by various
operating characteristics, e.g., rotational speed N of the internal
combustion engine, quantity of fuel QK injected and/or certain
temperature values T, in particular for the exhaust gas
temperature.
[0041] In addition, it is possible to check on whether a certain
period of time has elapsed since the last adjustment and/or whether
a certain driving performance of the internal combustion engine
and/or the exhaust-gas aftertreatment system has been achieved.
[0042] If query 320 detects that a suitable operating state does
not exist, the program is terminated in step 325. If a suitable
operating state prevails, then in step 330 the output signal of
suitable sensors is analyzed. Measured variables characterizing the
effect of the exhaust-gas aftertreatment system are preferably
detected here. For example, in the case of the supply of urea, the
ammonia content in the exhaust gas downstream from the exhaust-gas
aftertreatment system, in particular downstream from the reduction
catalytic converter, may be analyzed. In addition, it is possible
for the nitrogen oxide concentration, i.e., the concentration of
unwanted substances that are to be eliminated by the exhaust-gas
aftertreatment system, to be detected by a sensor.
[0043] In the next step 340, a lower threshold value US is
preselected as a function of the operating state of the internal
combustion engine and/or the exhaust-gas aftertreatment system.
Similarly, an upper threshold value OS is also preselected as a
function of these variables. The state variable is preferably the
rotational speed, quantity of fuel injected QK and, if necessary,
other variables such a temperature values T characterizing the
exhaust gas temperature.
[0044] In a simplified embodiment, it is possible to provide for
fixed values to be specified, this method being implemented only at
certain operating points at which the NH.sub.3 and NO.sub.x signals
assume the expected values.
[0045] Then in step 350 a check is performed to determine whether
the output signal of the ammonia sensor is greater than the upper
threshold value. If this is the case, then in step 360 a correction
value is defined, resulting in a decrease of the quantity of
reducing agent supplied. For example, it is possible to provide for
a negative correction value to be supplied or for the output value
of the signal preselected to be multiplied by a value less than 1.
Then the program likewise ends in step 325.
[0046] If query 350 detects that the output signal of ammonia
sensor 192 is lower than the upper threshold value OS, then
subsequent query 370 checks on whether the output signal of the
sensor is smaller than lower threshold value US. If this is the
case, then in step 380 a correction value is preselected so that it
produces an increase in the quantity of reducing agent
supplied.
[0047] In the alternative embodiment, it is possible to provide for
a check to be performed in step 370 to determine whether the
NO.sub.x output signal of a nitrogen oxide sensor 193 is greater
than a threshold value US, in which case a correction is also
performed to increase the quantity of reducing agent. Accordingly,
it is also possible to proceed in the case of query 350 such that
the output signal of a NO.sub.x sensor is checked to determine
whether it is lower than a threshold value and in this case the
quantity of reducing agent is decreased.
[0048] According to the present invention, in certain states of the
internal combustion engine and/or the exhaust-gas aftertreatment
system, the measured variable characterizing the effect of the
exhaust-gas aftertreatment system is compared with expected values
and the quantity of reducing agent is corrected on the basis of
this comparison.
[0049] It is possible for the output signal of the signal
preselection unit to be corrected or for the signal preselection to
be altered, i.e., the values stored in the engine characteristics
maps, for example, to be altered accordingly. In particular, the
quantity of reducing agent is decreased when the quantity of
ammonia exceeds an upper threshold value and/or the quantity of
reducing agent is increased when the quantity of nitrogen oxide
exceeds an upper threshold value.
[0050] According to the present invention, systems having only one
ammonia sensor or one nitrogen oxide sensor are used, but as an
alternative it is also possible to provide systems with an ammonia
sensor and a nitrogen oxide sensor. It is particularly advantageous
to use a nitrogen oxide sensor which may also be used for other
functions in the area of controlling the internal combustion engine
and/or the exhaust-gas aftertreatment system.
[0051] The procedure according to the present invention is not
limited to systems which use urea or a similar compound as a
reducing agent, in particular when a nitrogen oxide sensor is used,
but instead it may also be used with other systems which employ
different reducing agents. In particular, it is possible to provide
for hydrocarbons to be supplied as reducing agents to the exhaust
gas. This is possible in particular using an actuator member 182.
As an alternative, it is also possible to meter hydrocarbons, which
are used in particular as fuel supplied via conventional actuator
elements 180 for controlling the quantity of fuel injected into the
internal combustion engine. Thus, for example, it is possible to
provide for a secondary injection to introduce the corresponding
hydrocarbons into the exhaust gas.
* * * * *